The present invention relates to the field of diagnosis and prognosis. More particularly, the present invention relates to methods of and kits for (i) determining a risk of a subject to develop cancer; (ii) evaluating an effectiveness and preferred dosage of cancer therapy administered to a cancer patient; and (iii) determining a presence of correlation or non-correlation between an activity of at least one DNA repair enzyme and at least one cancer.
The DNA in each cell of a body is constantly subjected to damage caused by both internal (e.g., reactive oxygen species) and external DNA damaging agents (e.g., sunlight, X- and γ-rays, smoke) (Friedberg, et al., 1995). Most lesions are eliminated from DNA by one of several pathways of DNA repair (Friedberg, et al., 1995, Hanawalt, 1994, Modrich, 1994, Sancar, 1994). When unrepaired DNA lesions are replicated, they cause mutations because of their miscoding nature (Echols and Goodman, 1991, Livneh, et al., 1993, Strauss, 1985). The occurrence of such mutations in critical genes, e.g., oncogenes and tumor suppressor genes, may lead to the development of cancer (Bishop, 1995, Vogelstein and Kinzler, 1993, Weinberg, 1989). Indeed, DNA repair has emerged in recent years as a critical factor in cancer pathogenesis, as a growing number of cancer predisposition syndromes have been shown to be caused by mutations in genes involved in DNA repair and the regulation of genome stability. These include Xeroderma Pigmentosum (Weeda, et al., 1993), Hereditary nonpolyposis colon cancer (Fishel, et al., 1993, Leach, et al., 1993, Modrich, 1994, Parsons, et al., 1993), Ataxia Telangiectasia (Savitsky, et al., 1995), Li-Fraumeni syndrome (Srivastava, et al., 1990), and the BRCA1 (Gowen, et al., 1998, Scully, et al., 1997) and BRCA2 genes (Connor, et al., 1997, Patel, et al., 1998, Sharan, et al., 1997). In these cases, which represent a minority of the cancer cases, gene mutations have caused malfunction, leading to a strong reduction in DNA repair.
A possible extension of the role of DNA repair in hereditary cancer, would be a role for DNA repair in sporadic cancer. Several studies suggested that inter-individual variability in DNA repair correlates with variation in cancer susceptibility, with low repair correlated to higher cancer risk (Athas, et al., 1991, Helzlsouer, et al., 1996, Jyothish, et al., 1998, Parshad, et al., 1996, Patel, et al., 1997, Sagher, et al., 1988, Wei, et al., 1996, Wei, et al., 1993, Wei, et al., 1994).
7,8-dihydro-8-oxoguanine (also termed 8-oxoguanine or 8-hydroxyguanine; dubbed 8-OxoG) is formed in DNA by two major pathways: (a) Modification of guanine in DNA by reactive oxygen species formed by intracellular metabolism, oxidative stress, cigarette smoke, or by radiation (Asami, et al., 1997, Gajewski, et al., 1990, Hutchinson, 1985, Leanderson and Tagesson, 1992). (b) Incorporation into DNA by DNA polymerases of 8-oxo-dGTP, which is formed by oxidation of intracellular dGTP (Maki and Sekiguchi, 1992). Once in DNA, 8-oxoG is replicated by DNA polymerases with the misinsertion of dAMP, causing characteristic GC to TA transversions (Shibutani, et al., 1991, Wood, et al., 1990). When the modified dGTP is used as a substrate by DNA polymerases, it is often misinserted opposite an A in the template, causing AT to CG transversions (Pavlov, et al., 1994).
The major route for removing 8-oxoG from DNA is base excision repair, initiated by 8-oxoguanine DNA N-glycosylase, product of the OGG1 gene (in humans termed also hOGG1; (Aburatani, et al., 1997, Arai, et al., 1997, Bjoras, et al., 1997, Radicella, et al., 1997, Roldan-Arjona, et al., 1997, Rosenquist, et al., 1997). The OGG1 gene was recently knocked-out in mice, such that the effects on carcinogenesis can now be examined in this organism (Klungland, et al., 1999, Minowa, et al., 2000). Expression of the E. coli enzyme in Chinese hamster cells reduced 4-fold the mutagenicity of γ radiation (Laval, 1994), indicating that the repair of 8-oxoG is important in negating the mutagenic activity of γ radiation. The following observations associate OGG1 with cancer: (i) OGG1 was mapped to chromosome 3p25, a site frequently lost in human lung and kidney cancers (Arai, et al., 1997, Audebert, et al., 2000, Ishida, et al., 1999, Lu, et al., 1997, Wikman, et al., 2000). (ii) OGG1 was found to be mutated in 2 out of 25 lung tumors (Chevillard, et al., 1998), and in 4 out of 99 renal tumors (Audebert, et al., 2000). (iii) OGG1 was found to be mutated in a leukemic cell line (Hyun, et al., 2000) and in a gastric cell line (Shinmura, et al., 1998). (iv) Analysis of p53 mutations in human lung, breast, and kidney tumors revealed a substantial occurrence of GC to TA mutations, a mutation type produced by unrepaired 8-oxoG (Hollstein et al., 1996; Hernandez-Boussard, et al., 1999).
Since preventive measures which reduce the risk of developing cancer, such as, but not limited to, the use of anti-oxidants, diet, avoiding cigarette smoking, refraining from occupational exposure to cancer causing agents, are known and further since periodic testing and therefore early detection of cancer offers improved cure rates, there is a great need for, and it would be highly advantageous to have methods and kits for determining a risk of a subject to develop cancer.
Since the effectiveness of cancer therapy depends on the sensitivity of cells to genotoxic (mutageic) agents, there is a great need for, and it would be highly advantageous to have methods and kits for evaluating an effectiveness and preferred dosage of cancer therapy administered to a cancer patient.
There is also a great need for, and it would be highly advantageous to have methods and kits for determining a presence of correlation or non-correlation between an activity of at least one DNA repair enzyme and at least one cancer, so as to allow to determine a risk of a subject to develop cancer and to evaluate an effectiveness and preferred dosage of cancer therapy administered to a cancer patient.